1. Field of the Invention
This invention relates to a navigation device, a map displaying method and an image display device with excellent operability.
2. Description of the Related Art
Recently, navigation devices which can find their own positions and traveling speeds in real time by using GPS (Global Positioning System) satellites orbiting up in the skies have been becoming popularized for being carried on a mobile unit such as an automobile or for portable use.
In a navigation device, a map based on electronic map data is displayed on its monitor. Particularly, a navigation device for being carried on a mobile unit has a function to guide in a traveling direction based on a route set by a user.
When setting a route, the user designates at least a starting point and a destination. Then, the navigation device searches for and generates an optimum route connecting the designated starting point and destination, and presents it to the user as a recommended route. The user can also arbitrarily designate a place where the user wants to visit before reaching the destination, or a landmark for traveling such as an intersection, interchange or ramp, as an en route spot. In this case, it is possible to designate a plurality of places as en route spots. When en route spots are thus designated by the user, the navigation device searches for an optimum route connecting the starting point, one or more en route spots and the destination.
Even when the user does not designate any particular en route spot, the navigation device can present a point located between the starting point and the destination as an en route spot when presenting a recommended route to the user. Thus, the user can grasp the way and an image of a guide point before leaving.
Moreover, in Japan, VICS (Vehicle Information and Communication System) has been becoming popularized as a system for providing real time traffic information such as traffic congestion, accidents, traffic control and parking lots by using beacon signs (information communication facilities) installed on the roads or FM (frequency modulation) multiplex broadcasting. A navigation device equipped with a unit for receiving such VICS information can display information of traffic obstruction and congestion due to traffic control and accidents on the basis of the VICS information, in the form of teletext information or graphic information on its monitor. This provides traffic congestion information corresponding to the traveling direction of the vehicle, that is, the recommended route, and therefore the user can properly get not only the traffic congestion information related to the road on which the user is currently traveling, but also the traffic congestion information with respect to the en route spot and the vicinity of the destination.
As described above, the navigation device provide various information which is highly convenient to the user. This information is based on map information. Maps displayed on the navigation device can be classified into detailed map and wide-area map. The maps can be displayed by a one-screen display technique for displaying one map on one screen, or by a two-screen display technique for displaying two maps on one screen.
FIG. 1 shows an example of the one-screen display of the detailed map. The one-screen display of the detailed map is effective for accurately identifying an intersection where the vehicle is to turn, or for recognizing the form of the road on which the vehicle is currently traveling. However, the one-screen display only provides information of an area relatively close to the vehicle and therefore it is not convenient for seeing the traveling route to the destination.
FIG. 2 shows an example of the one-screen display of the wide-area map. The one-screen display of the wide-area map is effective for recognizing the traveling route to the destination. However, the user may not accurately recognize an intersection where the vehicle is to turn. In short, the one-screen display of the detailed map and the one-screen display of the wide-area map have opposite advantages and drawbacks.
Thus, as shown in FIG. 3, the two-screen display technique is employed in which the detailed map and the wide-area map are displayed in parallel on a display screen. The two-screen display technique is proposed to provide map information having the advantages of both the detailed map and the wide-area map. However, it has not yet achieved desired effects for the following reason.
Specifically, since each of the maps displayed by the two-screen display technique only displays a part of a map which would be displayed by the one-screen display technique, the detailed map and the wide-area map cover only narrow areas, respectively. Therefore, the quantity of information provided by each map is smaller than that of the one-screen display. The advantages of the detailed map and the wide-area map cannot be exhibited sufficiently and the position of the vehicle carrying the navigation device may not be grasped accurately.